Methods and devices for manufacturing components by soaking with a flowable matrix material are fundamentally known. They are employed, e.g., for soaking monolithic components such as, for instance, dry fiber composite semifinished products, so-called preforms, with a matrix material such as, e.g., resin. Alike method is known, for instance, as a so-called Resin Film Infusion (RFI) method in which, for example, dry carbon fibers (CFRP). CFRP tissues or CFRP fabrics are inserted in a curing device and applied from the outside with a defined quantity of non-liquid resin film. Under the influence of pressure and temperature the corresponding resin fabric liquefies while soaking the previously applied carbon fibers or the tissue or fabric, respectively.
This known method has already been developed further by using liquid resin for soaking the tissue or fabric. Besides injection methods for the resin that have to employ very high pressure, in particular injection pressures of greater than 6 bar, a so-called “infusion method” in various configurations is already known for manufacturing components by flowable matrix material. Such infusion methods are known, for example, under the terms VARTM (Vacuum Assisted Resin Transfer Molding), MVI (Modified Vacuum Infusion), SCRIMP (Seemann Composite Resin Infusion Molding Process), CAPRI (Controlled Atmospheric Pressure Resin Infusion Process), or VAP (Vacuum Assisted Process). All of these processes have in common that a dry semifinished product tissue or fabric, for example a tissue of CFRP, is inserted in an open tool and covered by a flowing aid and optionally a semi-permeable membrane or sheet above the latter. This membrane is semi-permeable and thus gas-permeable but impermeable to matrix material. Above this a further sheet is draped which—in addition to the impermeability to matrix material—is furthermore gas-impermeable. It is possible to apply a vacuum between these two sheets, so that matrix material that is infused into the inner space, in particular into the flowing aid, is drawn through the fabric or tissue equally positioned in the inner space, to thus soak the latter transversely to the main direction of flow. The infusion process basically has the advantage of requiring to work with negative pressure exclusively, so that it is possible to avoid costly and constructively complex tools which must withstand an overpressure that had been necessary, for example, in the previously used injection process.
In the framework of the development of components, in particular main load-bearing components such as, e.g., in aircraft construction, it has meanwhile become desirable to produce double-layer structural or sandwich components in order to save weight. These are to present a sandwich structure, wherein an upper and a lower skin layer is formed of a semifinished product tissue having the form of dry fabrics, for example CFRP fabrics or tissues, are formed by soaking the latter with a flowable matrix material. In between, in the manner of a core of the sandwich structure, as it were, a foam core is to be formed of a previously inserted core layer. Here the connection of the individual layers among each other is also brought about by a flowable matrix material, namely, by connection layers which form in the course of curing of the matrix material. In order to further improve the like sandwich structures with regard to the reception of loads and damage tolerance capability, attempts are also undertaken to reinforce the core layer and/or the individual skin layers with reinforcement devices. These are, for example, pin-type reinforcements that extend at least through the core layer.
In the manufacture of sandwich components by the known infusion processes it was, however, found that cracks form when sandwich components manufactured in this way are subjected to loads and lead to a defect of such a sandwich component. Moreover, changes in the material and cracks, or capillary fissures, were found even directly after the manufacturing process in the section of the sandwich component. Such an increased susceptibility to cracking is not acceptable for sandwich components in their use, in particular in the field of aircraft industry. In addition it was found that the reinforcement devices such as the pins, for example, are partly impaired due to buckling during the manufacturing process, whereby even the reinforcement properties of the sandwich components showed negative changes.
From DE 10 2005 003 713 A1 a method for manufacturing fiber-reinforced hollow core sandwich components in a vacuum-supported resin infusion process is known. Here an open-cell core material such as, e.g., a honeycomb core with two resin systems is used, wherein the first resin acts as a separating sheet which prevents penetration of the second resin into the honeycomb cells.
From WO 2010/007162 A1 a method for manufacturing a hollow body such as, e.g., a pipe of fiber-reinforced plastic is known, wherein a carrier is used on which reinforcing fibers are disposed and then molded with a plastic matrix. Subsequently the carrier is dissolved in a liquid in order to separate it from the finished hollow body.
From DE 10 2009 010 692 A1 a device for carrying out a RTM method for the manufacture of a structural component is known. This device comprises a process sensing mechanism including a thermal sensor allowing to monitor the manufacturing process.
From DE 10 2007 039 126 A1 a compound panel including honeycombs and an apparatus for its manufacture of SMC is known. The apparatus comprises a press. The press comprises two guide rods carried by a bottom part which carry a pressing cylinder and wherein a pressing die acted upon by the pressing cylinder and the piston thereof is guided, which in turn carries a tool upper part cooperating with a tool lower part seated on the bottom part.